It has been recognized for over 25 years that the development of a dysregulated inflammatory response as well as lung injury (ARDS) and multiple organ failure complicates the recovery of patients with severe trauma. During the previous funding period, we tested and validated the hypothesis that gut-derived factors, contained in the mesenteric lymph are key factors in the pathogenesis of acute lung injury in animals subjected to trauma-hemorrhagic shock (T/HS). Having shown that factors contained in T/HS lymph appear to be necessary for acute trauma-hemorrhagic shock-induced lung injury and that lung injury appears to be mediated through T/HS lymph-induced endothelial cell-neutrophil interactions, we are now proposing to identify the factors in T/HS mesenteric lymph that are responsible for T/HS lymph-induced endothelial cell injury. Thus in AIM 1 we propose to continue studies directed at isolating and characterizing the factors in T/HS lymph responsible for endothelial cell apoptosis, as well as increased endothelial permeability and adhesion molecule expression. Understanding the mechanisms by which T/HS lymph leads to endothelial cell injury and death are of biologic and potential clinical importance, thus, in AIM 2, we propose to investigate the pathways and mechanisms by which T/HS lymph causes endothelial cell apoptosis. We have chosen to focus our efforts on the endothelial cell, because the endothelium is recognized as being a central effector of the immuno-inflammatory response and endothelial activation/injury contributes to organ injury. If our global hypothesis that gut-derived factors contained primarily in the mesenteric lymph potentiates the development of distant organ injury is correct, it would clarify several important issues. First, since the heart and lungs are the first two organs exposed to mesenteric lymph (i.e. lymph enters subclavian vein via thoracic duct), it would help explain why the lung is the first organ to fail in severely injured patients as well as clarify the discordant results between some experimental and clinical studies on the role of the gut in MODS. Additionally, these studies will provide new and unique information on the biology of T/HS-induced endothelial cell injury, which can direct future therapeutically-driven investigations, since T/HS lymph is a clinically relevant biologic fluid that is directly involved in transducing the hypotensive effects of trauma-hemorrhage into a proinflammatory and tissue injurious signal. PUBLIC HEALTH RELEVANCE: For over 25 years it has been recognized that the development of a dysregulated inflammatory response and associated lung and multiple organ failure have complicated the recovery of patients with severe trauma and remain one of the most common causes of death in the ICU. Our work for the first time has identified the source of those factors leading to this organ failure state and thus understanding their generation and actions is highly likely to lead to new therapeutic strategies.